Dynamic pressure bearing and method of manufacturing the same

ABSTRACT

In a dynamic pressure bearing, when a step portion ( 1   a ) is formed on the inner peripheral surface ( 1   b ) of a sleeve ( 1 ) and radial dynamic pressure grooves ( 3 ) are formed on the inner peripheral surface of the step portion, the width (L) in the axial direction of the dynamic pressure grooves is set to be slightly smaller than the width (D) in the axial direction of the step portion. The dynamic pressure grooves of the sleeve are formed by electrolytic etching.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a dynamic pressure bearing, andparticularly to a dynamic pressure bearing having dynamic pressuregrooves formed on the inner peripheral surface of a sleeve in which ashaft is fitted, which has high precision, reduces the manufacturingcost and has a lower bearing damage rate, and a method of manufacturingthe dynamic pressure bearing.

[0002] A dynamic pressure bearing, in which a shaft is fitted in asleeve and relatively rotated and herringbone type or spiral typegrooves are formed on at any one of the inner peripheral surface of thesleeve and the outer peripheral surface of the shaft, is used as abearing apparatus for a spindle motor rotating at high speed ininformation equipment or the like.

[0003] For example, as shown in FIG. 9, there is used such a dynamicpressure bearing that herringbone type dynamic pressure grooves 23 areformed on the inner peripheral surface of a sleeve 21 on which a statorcoil 21 is mounted, a shaft 25 is fitted in the sleeve 21 so that aferromagnetic material (not shown) is disposed to face the stator coil20 and the stator coil 20 is supplied with current to rotate the shaft25 at high speed. Such a dynamic pressure bearing is used in anapparatus in which a polygon mirror or optical disc (not shown) is fixedto the shaft 25 and a laser beam is reflected therefrom to record orread out information.

[0004] On the inner peripheral surface 21 b of the sleeve 21, a bearingportion 22 is equipped at a step portion 21 a having a slightly reduceddiameter, and herringbone type or spiral type V-shaped dynamic pressuregrooves 23 are formed on the inner surface of the bearing portion 22 ofthe step portion 21 a as shown in FIGS. 10 and 11. Alternatively,dynamic pressure grooves may be formed on the outer peripheral surfaceof the shaft 25 in place of formation of the dynamic pressure grooves 23on the inner peripheral surface of the sleeve 21. Such dynamic pressuregrooves 23 are usually formed by plastic working based on form rolling.Further, there is known an example of forming dynamic pressure groovesby using an electrolytic etching working in order to satisfy recentrequirements for high precision and increase of working speed. In thecase of stainless steel, etc., etching working on these materials needsmuch time. Therefore, there has been proposed a dynamic pressure-bearingachieved by subjecting a bearing face of a sleeve of aluminum alloy toplastic working based on ball form rolling and carrying out an alumitetreatment after honing working, thereby forming an anode oxidationcoating (Japanese Laid-open Patent Application No. Hei-8-247138).

[0005] To overcome lack of lubricating oil in bearing gaps to enhancedurability and bearing rigidity, such a dynamic pressure bearing isproposed that it includes dynamic pressure grooves formed on the innerperipheral surface of the sleeve, lubricating oil or grease isimpregnated in the bearing body 31, and dynamic pressure grooves 33 areformed to be inclined with respect to the bearing face of the bearingbody as shown in FIG. 12A (Japanese Laid-open Patent Application No.Hei-11-82479). According to the bearing apparatus thus constructed, therotational shaft is supported under a non-contact state by dynamicpressure films of the lubricating oil formed in the bearing gaps, andthe lubricating oil is circulated between the inside of the bearing body32 and each bearing gap through opening portions of the bearing face. Inthis case, as shown in FIG. 12B, each dynamic pressure groove 33comprises one oblique groove 33 a, the other oblique groove 33 b and asmoothing portion 34 formed between the oblique grooves 33 a and 33 b.

[0006] As described above, the dynamic pressure grooves 23 of thebearing portion 22 equipped at the step portion 21 a of the innerperipheral surface of the conventional sleeve 21 are formed over thewhole width D from one end portion 21 c of the step portion 21 c to theother end portion of the step portion 21 c. Therefore, as shown in FIG.11, particularly when the shaft 25 is rotated in a bell-shaped mode(conical mode or precession mode) at the start or stop time of themotor, the shaft 25 damages the end portions 21 c of the step portion 21a. If the end portions 21 c of the step portion 21 a at which thebearing portion 22 is equipped are repetitively damaged due to rotationof the shaft 25 in such a conical mode as described above, theperformance as the dynamic pressure bearing is degraded, and finally itadversely affects the performance and lifetime of equipment equippedwith such a dynamic pressure bearing.

[0007] According to the conventional technique, after dynamic pressuregrooves 23 are formed on the inner peripheral surface of a sleeve by theplastic working based on the form rolling as described above, it isrequired to carry out finish machining by reaming, balling, horning orthe like, so that the manufacturing cost is high.

[0008] The etching process used as a work to form dynamic pressuregrooves has high precision, however, it still needs a high manufacturingcost. Further, dynamic pressure grooves may be formed by theelectrolytic etching processing. However, the conventional processinghas a problem that pattern symmetry is lost unless the positioning to awork is not performed at high precision, so that fluid flow occurs.

SUMMARY OF THE INVENTION

[0009] The present invention has been implemented to overcome theforegoing problem, and has an object to provide a dynamic pressurebearing which can reduce damages of dynamic pressure grooves even when ashaft has a swinging motion in a conical mode, simplify the positioning(precision) to keep symmetry in an electrolytic etching process andexhibit high performance, and a method of manufacturing the dynamicpressure bearing.

[0010] In order to solve the aforesaid object, the invention ischaracterized by having the following arrangement.

[0011] (1) A dynamic pressure bearing comprising:

[0012] a sleeve;

[0013] a bearing portion formed on an inner peripheral surface of thesleeve, wherein a diameter of an inner peripheral surface of the bearingportion is smaller than the inner diameter of the sleeve; and

[0014] dynamic pressure grooves formed on a part of the inner peripheralsurface of the bearing portion, wherein the dynamic pressure groove isnot formed at opposite end portions of the bearing portion.

[0015] (2) A method of manufacturing a dynamic pressure bearingincluding a sleeve; a bearing portion formed on an inner peripheralsurface of the sleeve, having a predetermined width, wherein thediameter of the inner peripheral surface of the bearing portion issmaller than the inner diameter of the sleeve; and dynamic pressuregrooves formed on a part of the inner peripheral surface of the bearingportion, wherein the dynamic pressure groove is not formed at oppositeend portions of the bearing portion, the method comprising the step of:

[0016] subjecting the sleeve to electrolytic etching to form the dynamicpressure groove.

[0017] (3) A dynamic pressure bearing comprising:

[0018] a sleeve;

[0019] a bearing portion formed on an inner peripheral surface of thesleeve, having a first width in an axial direction, wherein a diameterof an inner peripheral surface of the bearing portion is smaller than aninner diameter of the sleeve; and

[0020] dynamic pressure groove formed on the inner peripheral surface ofthe bearing portion, having a second width in the axial directionsmaller than the first width.

[0021] (4) The dynamic pressure bearing according to (3), wherein thedynamic pressure groove is not formed at opposite end portions of thebearing portion.

[0022] (5) The dynamic pressure bearing according to (3), wherein acenter line of the first width is coincident with a center line of thesecond width.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a partially perspective view showing a sleeveconstituting a dynamic pressure bearing according to the presentinvention;

[0024]FIG. 2 is a cross-sectional view in the axial direction of thesleeve constituting the dynamic pressure bearing according to thepresent invention;

[0025]FIG. 3 is a diagram showing the construction of a resistelectrodeposition apparatus to form a resist, which is a pre-treatmentstage to form dynamic pressure grooves on the inner peripheral surfaceof the sleeve constituting the dynamic pressure bearing according to thepresent invention;

[0026]FIG. 4 is a diagram showing a method of manufacturing the dynamicpressure bearing according to the present invention, which is across-sectional view showing the sleeve under the state that insulatingmaterial is coated on a pattern of the dynamic pressure grooves byprinting or masking corresponding to a pre-treatment processing methodfor the dynamic pressure grooves to be formed by electrolytic etching;

[0027]FIG. 5 is a diagram showing the method of manufacturing thedynamic pressure bearing according to the present invention, which is across-sectional view showing the state that a resist is electricallydeposited on the sleeve coated with the insulating material;

[0028]FIG. 6 is a diagram showing the method of manufacturing thedynamic pressure bearing according to the present invention, which is across-sectional view of the sleeve before the insulating material coatedon the inner peripheral surface of the sleeve is removed to form thepattern of the dynamic pressure grooves and put into an electrolyticetching apparatus;

[0029]FIG. 7 is a diagram showing the construction of the electrolyticetching apparatus when electrolytic etching is carried out on the sleevehaving the etching pattern of the dynamic pressure grooves;

[0030]FIG. 8 is a cross-sectional view in the axial direction of thesleeve constituting the dynamic pressure bearing according to thepresent invention;

[0031]FIG. 9 is a diagram showing the construction of a conventionaldynamic pressure bearing used for a spindle motor;

[0032]FIG. 10 is a partially perspective view showing a sleeveconstituting the conventional dynamic pressure bearing;

[0033]FIG. 11 is a cross-sectional in the axial direction of the sleeveconstituting the conventional dynamic bearing; and

[0034]FIG. 12A is a cross-sectional view showing the sleeve constitutingthe conventional dynamic pressure bearing, and FIG. 12B is across-sectional view showing the sleeve of the conventional dynamicpressure bearing, which is also a cross-sectional view when a dynamicbearing portion is equipped at two places.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Preferred embodiments according to the present invention will bedescribed hereunder with reference to the accompanying drawings.

[0036]FIG. 1 is a partially perspective view showing a sleeve 1constituting a dynamic pressure bearing according to the presentinvention, and FIG. 2 is a cross-sectional view in the axial directionof the sleeve 1.

[0037] As shown in FIGS. 1 and 2, a step portion 1 a having apredetermined width is formed on the inner peripheral surface 1 b of thesleeve 1 so that the diameter of the inner peripheral surface thereof issmaller than the inner diameter of the sleeve 1, and a bearing portion 2is formed on the inner peripheral surface of the step portion 1 a.Herringbone type dynamic pressure grooves 3 are formed at the bearingportion 2. The dynamic pressure grooves 3 may be designed in a spiraltype or V-shape type. In this case, the width L of the dynamic pressuregrooves 3 in the axial direction of the sleeve is slightly smaller thanthe width D of the step portion 1 a (L <D). A shaft 25 (see FIGS. 9 and11) is inserted and fit in the inner diameter portion of the sleeve,thereby constituting a bearing portion of a spindle motor, for example.Accordingly, an inner peripheral surface on which no dynamic pressuregroove 3 is formed exists at both the end portions of the bearingportion 2 formed on the inner peripheral surface of the step portion 1a.

[0038] In the dynamic pressure bearing of the present invention, sincethe width L in the axial direction of the dynamic pressure grooves 3 issmaller than the width D in the axial direction of the step portion 1 aon the inner peripheral surface of the sleeve 1, the performance of thebearing portion 2 would suffer no adverse effect even if the shaft comesinto contact with the end portion 1 c of the step portion 1 a. That is,the conventional dynamic pressure bearing shown in FIG. 11 has theproblem that the shaft 25 comes into contact with the end portions 21 cof the step portion 21 a and thus damages the dynamic pressure grooves 3due to the swinging motion (precession or the like) of the shaft 25 whenthe motor is started or stopped. However, according to the dynamicpressure bearing of the present invention, even when the shaft makes aswinging motion (precession or the like), the dynamic pressure grooves 3have no damage because each of both the end portions 1 c of the stepportion 1 a and the end portion 3 a of each dynamic pressure groove 3are spaced away from each other at a fixed distance through a flatportion. Accordingly, the pattern symmetry of the dynamic pressuregrooves 3 is prevented from being lost and occurrence of fluid flow isprevented, so that the performance of the dynamic pressure bearing 2suffers no effect.

[0039] Next, a method of forming the dynamic pressure grooves 3 on theinner peripheral surface of the sleeve 1 will be described.

[0040]FIG. 3 shows the construction of a resist electrode positionapparatus for a resist forming process, which corresponds to apre-treatment stage to form the dynamic pressure grooves 3 on the innerperipheral surface of the step portion 1 a equipped on the innerperipheral surface of the sleeve 1.

[0041] As shown in FIG. 3, the resist electrodeposition apparatusincludes an electrodeposition tank 5, resist-component containingelectrodeposition liquid 4 stocked in the electrodeposition tank 5 and apower source 6 having a cathode and an anode. The sleeve 1 is connectedto the cathode side of the power source 6 and immersed in theelectrodeposition liquid 4. A positive electrode rod 7 is connected tothe anode side.

[0042]FIG. 4 shows a pre-treatment processing method of the dynamicpressure grooves 3 on the basis of electrolytic etching.

[0043] First, a pattern of the dynamic pressure grooves 3 is printed onthe inner peripheral surface of the sleeve 1 connected to the cathodeside by coating insulating material 8. This printing may be performed byusing paper pattern or mask which is designed in conformity with theinner diameter of the step portion 1 a formed on the inner peripheralsurface of the sleeve 1, or by using relief printing, offset printing orthe like.

[0044] When the sleeve 1 thus coated with the insulating material 8 asthe pattern of the dynamic pressure grooves 3 is connected to thecathode side of the power source, the positive electrode rod 7 isconnected to the anode side and current flows into the sleeve 1, anelectrodeposition resist layer 9 is formed at portions other than theportions coated with the insulating material 8 as shown in FIG. 5. Byremoving the insulating material 8 under this state, an etching patternis formed by the electrodeposition resist layer as shown in FIG. 6. Inplace of formation of the insulating material 8, there may be used amethod of forming a resist layer 9 on the whole inner peripheral surfaceof the step portion la without forming any insulating material 8 andthen removing an etching pattern portion corresponding to the dynamicpressure grooves 3 from the resist layer 9 by a laser, thereby formingan etching pattern.

[0045] Next, the electrolytic etching method will be described.

[0046]FIG. 7 shows the construction of an electrolytic etching apparatuswhen electrolytic etching is conducted on the sleeve having the etchingpattern of the dynamic pressure grooves formed thereon.

[0047] The electrolytic etching apparatus includes an electrolytic tank11, electrolytic liquid 10 stocked in the electrolytic tank 11, and apower source 13 connected to the sleeve 1 at the anode side thereof andto an electrode rod 12 at the cathode side thereof. Electrolytic liquid10 such as sodium chloride (NaCl), sodium nitrate (NaNO₃) or the like isstocked in the electrolytic tank 11. When the sleeve 1 having apredetermined pattern of dynamic pressure grooves 3 is immersed in theelectrolytic liquid 10 and current is made to flow into the sleeve 1,only the metal surface of the sleeve 1 on which the pattern of thedynamic pressure grooves 3 is formed is dissolved through anelectrolytic reaction to form the dynamic pressure grooves 3.Thereafter, by removing the electrodeposition layer 9, the dynamicpressure grooves based on the electrolytic etching method are formed.

[0048] As described above, in the dynamic pressure bearing of thepresent invention, the dynamic pressure grooves 3 are formed on theinner peripheral surface of the step portion 1 a of the sleeve 1 by theabove method, and the width L in the axial direction of the dynamicpressure grooves 3 is set to be slightly smaller than the width D in theaxial direction of the step portion 1 a. In this case, it is ideal thatthe center line O₀ of the width L in the axial direction of the dynamicpressure grooves 3 is coincident with the center line O₀ of the width inthe axial direction of the step portion 1 a. However, in the case of thepresent invention, the performance of the dynamic pressure bearing 2suffers no adverse effect even if the center line O₁ of the width L inthe axial direction of the dynamic pressure grooves 3 cannot be madecoincident with the center line O₀ of the width D in the axial directionof the step portion 1 a and thus there exists some displacementtherebetween. That is, even if there exists some displacement betweenthe center line O₁ of the width L and the center line O₀ of the width Don the inner peripheral surface of the sleeve 1, the width L in theaxial direction of the dynamic pressure grooves 3 is slightly smallerthan the width D in the axial direction of the step portion 1 a and thusthis displacement (for example, the center of the dynamic pressuregrooves 3 is somewhat displaced) has no effect on the performance of thedynamic pressure bearing.

[0049] As described above, according to the dynamic pressure bearing ofthe present invention, the end portions of the dynamic pressure groovesare designed to be flat, so that the bearing performance is not degradedeven if the shaft is rotated in the conical mode. Further, even if theshaft abuts against the bearing when the shaft is rotated, the damageimposed on the dynamic pressure bearing is reduced.

[0050] Further, the method of manufacturing the dynamic pressure bearingis based on the electrolytic etching method, however, the symmetry ofthe dynamic pressure grooves is determined by the electrode. Therefore,the positioning precision of the work and the electrode during theprocessing is simplified, and also unlike the conventional technique, itis unnecessary to carrying out the processing while the positioningprecision of the electrode with respect to the work is kept high.

[0051] Still further, according to the electrolytic processing method ofthe present invention, there occurs no flash due to return or the likeunlike the manufacturing method based on the form rolling, and thus apost-processing step is unnecessary, so that the number of processingsteps can be reduced and thus the manufacturing cost can be reduced.

[0052] Still further, the symmetry of the dynamic pressure grooves isnot lost even by the rotation of the shaft in the conical mode, and thusno fluid flow occurs.

What is claimed is:
 1. A dynamic pressure bearing comprising: a sleeve;a bearing portion formed on an inner peripheral surface of the sleeve,wherein a diameter of an inner peripheral surface of the bearing portionis smaller than the inner diameter of the sleeve; and dynamic pressuregrooves formed on a part of the inner peripheral surface of the bearingportion, wherein the dynamic pressure groove is not formed at oppositeend portions of the bearing portion.
 2. A method of manufacturing adynamic pressure bearing including a sleeve; a bearing portion formed onan inner peripheral surface of the sleeve, having a predetermined width,wherein the diameter of the inner peripheral surface of the bearingportion is smaller than the inner diameter of the sleeve; and dynamicpressure grooves formed on a part of the inner peripheral surface of thebearing portion, wherein the dynamic pressure groove is not formed atopposite end portions of the bearing portion, the method comprising thestep of: subjecting the sleeve to electrolytic etching to form thedynamic pressure groove.
 3. A dynamic pressure bearing comprising: asleeve; a bearing portion formed on an inner peripheral surface of thesleeve, having a first width in an axial direction, wherein a diameterof an inner peripheral surface of the bearing portion is smaller than aninner diameter of the sleeve; and dynamic pressure groove formed on theinner peripheral surface of the bearing portion, having a second-widthin the axial direction smaller than the first width.
 4. The dynamicpressure bearing according to claim 3, wherein the dynamic pressuregroove is not formed at opposite end portions of the bearing portion. 5.The dynamic pressure bearing according to claim 3, wherein a center lineof the first width is coincident with a center line of the second width.